1. Field of the Invention
The present invention relates to a method for producing nanocarbon materials. More particularly, the present invention relates to a method which enables one to quantitatively produce nanocarbon materials from relatively inexpensive starting material by a simple manner using a relatively inexpensive reaction apparatus. The nanocarbon materials produced according to the present invention include carbon nanotubes, carbon nanofibers, and the like.
2. Related Background Art
Since the discovery of a fullerene C60 having a soccer ball-like polyhedral molecular structure comprising 60 carbon atoms by H. W. Kroto, R. E. Smallry and R. F. Curl, other fullerenes have been discovered, and various studies on their industrial application have been carrying out. Separately, since the discovery of a carbon nanotube (CNT) corresponding to a cylindrical molecule of a fullerene, specifically having a molecular structure in which a graphene sheet (a single atomic layer of crystalline graphite) rolled up into a cylinder by Iijima in 1991, other carbon nanotubes have been discovered. And it has been reported that these carbon nanotubes have an excellent electron emission performance, a function to store hydrogen therein, and a function to take up and store lithium therein and release said lithium in the electrochemical reaction. In view of this, researches have been conducting to use such carbon nanotubes as electrode materials in light emission devices such as FEDs (field emission displays), as electrode materials in rechargeable lithium batteries, as catalyst-retaining carbon materials in fuel cells, and as hydrogen storage materials in hydrogen storage systems.
As the method for producing such carbon nanotubes, there are known a method wherein arc-discharge is generated in an gas atmosphere containing a carbon material such as hydrocarbon, a method wherein a target comprising graphite is evaporated by irradiating a laser thereto, and a method wherein a gaseous carbon material comprising acetylene or the like is subjected to thermal decomposition on a substrate having a catalyst of cobalt metal or nickel metal arranged thereon.
Particularly, Japanese Laid-open Patent Publication 6(1994)-157016 discloses a method for producing carbon nanotubes, wherein arc-discharge is generated between a pair of carbon rods respectively as a positive electrode and a negative electrode in an inert gas atmosphere to deposit a carbon nanotubes-containing solid material on the negative electrode.
Japanese Laid-open Patent Publication P2000-95509A discloses a method for producing carbon nanotubes, wherein a rod-shaped positive electrode containing carbon and non-magnetic transition metal and a rod-shaped negative electrode comprising graphite are arranged such that their tips are opposed to each other and arc-discharge is generated between the tip of the positive electrode and that of the negative electrode in an inert gas atmosphere to deposit carbon nanotubes on the tip portion of the negative electrode.
Japanese Laid-open Patent Publication 9(1997)-188509 discloses a method for producing carbon nanotubes, wherein a carbon material and a metal catalyst are supplied into a high frequency plasma generated to deposit carbon nanotubes on a substrate.
Japanese Laid-open Patent Publication 9(1997)-188509 discloses a method for producing carbon nanotubes, wherein a graphite-containing carbon rod is positioned in a quartz tube arranged in an electric furnace and a laser is irradiated to said carbon rod in an inert gas atmosphere to deposit carbon nonatubes on the inner wall face of the quartz tube.
Japanese Laid-open Patent Publication P2000-86217A discloses a method for producing carbon nanotubes, wherein gaseous hydrocarbon is thermally decomposed on a catalyst comprising a molybdenum metal or a molybdenum metal-containing material to deposit carbon nanotubes on said catalyst.
However, any of the above-mentioned methods for producing nanocarbon materials (carbon nanotubes) has disadvantages such that the starting material and the apparatus used for practicing the method are costly and therefore a product obtained becomes unavoidably costly and it is difficult to quantitatively produce nanocarbon materials.
Separately, Carbon Vol. 36, No. 7-8, pp. 937–942, 1998 (Yury G. Gogotsi et al.) describes a method in that filamentous carbons are formed from paraformaldehyde by way of hydrothermal reaction at a temperature of 700 to 750° C. under 100 Mpa pressure for 150 hours.
Journal of Materials Research Society, Vol. 15, No. 12, pp. 2591–2594, 2000 (Yury Gogosi et als.) describes that multiwall carbon nanotubes are formed from polyethylene by way of pyrolysis of said polyethylene in the presence of nickel at a temperature of 700 to 800° C. under 60 to 100 Mpa.
Journal of American Chemical Society Vol. 123, No. 4, pp. 741–742, 2001 (Jose Maria Calderon et al.) describes a method wherein multiwall carbon nanotubes are formed from amorphous carbon by way of hydrothermal treatment of said amorphous carbon in the absence of a metal catalyst at a temperature of 800° C. under 100 Mpa pressure for 48 hours.
However, in any of the methods described in the above-described documents, because high pressure condition of 100 Mpa or 60 to 100 Mpa is adopted, a specific high pressure capsule made of Au (which is costly) and which can withstand such high pressure is used as the reaction vessel, and the starting material and water are introduced into said capsule wherein the starting material is subjected to hydrothermal reaction at a high temperature (700 to 800° C.) under high pressure condition of 100 Mpa or 60 to 100 Mpa. Therefore, a product obtained in any of the methods described in the above-described documents unavoidably becomes costly.
And any of the above-described documents does not teach or suggest a method which enables one to efficiently produce nanocarbon materials (including carbon nanotubes or filamentous carbons) under low pressure condition of less than 50 Mpa, using a relatively inexpensive pressure reaction vessel without necessity of using such costly pressure reaction vessel.
There is a demand for providing a method which enables one to quantitatively produce nanocarbon materials (including carbon nanotubes and carbon nanofibers), which are usable as electrode materials in devices such as FEDs (field emission displays), as electrode materials in rechargeable lithium batteries, as catalyst-retaining carbon materials in fuel cells, and as hydrogen storage materials in hydrogen storage systems, at a reasonable production cost from relatively inexpensive raw material by a simple manner under low pressure condition which does not require to use such specific and costly pressure reaction vessel as above described.